1. Field of the Invention
The present invention relates to a display device that includes an optical element array sheet that uses lenticular lenses or fly-eye lenses to provide image display directed in a plurality of view-points for implementing control of a three-dimensional display and angle of field; and to a portable terminal, a fabrication method of a display device, a fabrication method of a molding die, and a fabrication method of the optical element array sheet.
2. Description of the Related Art
With the growth of demand for higher functionality of display devices in recent years, display devices have been proposed that are realized by combining optical element array sheets such as lenticular lenses, prism sheets, or diffusion sheets in display panels that use electro-optical elements such as liquid crystal and that enable control over three-dimensional image display or angle of field.
A display device that uses a lenticular lens sheet is next described as one example of such a display device. FIG. 1 is a perspective view giving a schematic representation of a lenticular lens sheet, and FIG. 2 is a schematic view showing an example of the configuration of a display device that uses a lenticular lens sheet and a three-dimensional display method.
As shown in FIG. 1, lenticular lens sheet 110 is formed with one flat surface and the other surface formed by arranging a plurality of cylindrical lenses 111 in a series. Lenticular lens sheet 110 has cylindrical surfaces and is formed with semicircular profiles.
As shown in FIG. 2, left-eye pixels 115a and right-eye pixels 115b corresponding to the left eye and right eye, respectively, of an observer are arranged alternately on display panel 114 to correspond to the focal point of each cylindrical lens 111. In display panel 114, left-eye pixel 115a and right-eye pixel 115b are driven in accordance with a prescribed image signal by a drive circuit (not shown). In this way, cylindrical lenses 111 cause a left-eye image to be formed in left-eye region 120a and a right-eye image to be formed in right-eye region 120b, whereby a three-dimensional image can be shown to the observer of display panel 114. Of course, display panel 114 can also display a normal two-dimensional image by driving right-eye pixel 115a and left-eye pixel 115b by the same image signal.
Display devices that use lenticular lens sheets also include multi-image simultaneous display devices that display a plurality of images at the same time. In these display devices, respectively different images can be shown simultaneously to a plurality of observers by distributing images toward the direction where they can be observed by means of a cylindrical lens by the same method as the above-described three-dimensional display.
As one example of an optical element array sheet, Japanese Patent Application Laid-Open No. 2006-47709 discloses the configuration shown in FIG. 3.
In a display device that uses this type of microlens array or lenticular lens sheet, the display of a high-quality three-dimensional image or the simultaneous display of a plurality of images calls for highly accurate positioning and bonding of the lenticular lens sheet with respect to the display panel. In particular, even greater improvement of positioning accuracy is required for bonding an optical element array sheet to a display panel in a high-definition display device that is incorporated in a portable terminal such as a portable telephone or portable information terminal (PDA: Personal Digital Assistant).
However, regarding the process for bonding a display panel to a lenticular lens that is related to the present invention, investigation for achieving an improvement of the positioning accuracy and reliability of bonding resulted in the identification of problems as next described. Regarding an optical element array sheet of which a lenticular lens sheet is representative, FIGS. 4A and 4B are schematic figures of steps for bonding an optical element array sheet to a display panel. As shown in FIG. 4A, optical element retaining head 201 adopts a configuration provided with a vacuum suction mechanism or a configuration in which adhesive gum is provided as an adhesive material on the retaining surface of optical element retaining head 201. Optical element retaining head 201 uses the suction power realized by the vacuum suction mechanism or the adhesive power realized by the adhesive gum to hold optical element array sheet 101 as shown in FIG. 4A and bonds display panel 114 and optical element array sheet 101 with bonding layer 203 interposed as shown in FIG. 4B.
In a step preceding the mounting step shown in FIGS. 4A and 4B, a step is carried out of peeling a sheet to protect bonding layer 203 from bonding layer 203 in order to bond optical element array sheet 101 to display panel 114. In this step, bonding layer 203 is, for example, peeled from retaining sheet 205 by holding optical element array sheet 101 that is held on retaining sheet 205 by optical element retaining head 201, as shown in FIGS. 5A and 5B.
In addition, protective sheet 204 for protecting bonding layer 203 is provided on optical element array sheet 101 as shown in FIG. 6A. Accordingly, in this step, after optical element array sheet 101 is held by optical element retaining head 201, for example, peeling tape 207 is used to peel protective sheet 204 from bonding layer 203 by causing this peeling tape 207 to adhere to protective sheet 204 as shown in FIG. 6B.
If the holding strength upon optical element array sheet 101 realized by optical element retaining head 201 is insufficient at this time, when optical element array sheet 101 is to be peeled from retaining sheet 205 as shown in FIG. 5A, optical element array sheet 101 will not be retained by optical element retaining head 201 and optical element array sheet 101 cannot be peeled from retaining sheet 205. Alternatively, if the holding strength upon optical element array sheet 101 by optical element retaining head 201 is not sufficient in the step shown in FIGS. 6A and 6B, the problem arises that when protective sheet 204 for protecting bonding layer 203 is separated from peeling tape 207, optical element array sheet 101 will be held on the peeling tape side together with protective sheet 204 and will be detached from optical element retaining head 201.
In the optical element array sheet that uses lenticular lens 110 such as shown in FIG. 7, the type of contact in the contact portion of lenticular lens 110 and optical element retaining head 201 when the optical element array sheet is held by optical element retaining head 201 as shown in FIG. 8 is a linear contact as shown in FIG. 9. In a fly-eye lens such as shown in FIG. 10, the type of contact in the contact portion of the fly-eye lens and optical element retaining head 201 when an optical element array sheet is held by optical element retaining head 201 as shown in FIG. 11 is a point contact as shown in FIG. 12.
As a result, when an optical element array sheet is held by the adhesive strength realized by a gum material provided on an optical element retaining head, the adhesive strength is proportional to the area of contact between the optical element retaining head and the optical element array sheet, and sufficient holding strength is therefore not obtained. When an optical element retaining head provided with a vacuum suction mechanism is used to hold an optical element array sheet, because the surface of the optical element array sheet is not flat but rather formed by a plurality of curved surfaces, air leakage occurs at the surface of the optical element array sheet, whereby the suction strength is reduced and sufficient holding strength is not obtained.
Of the optical element array sheets that relate to the present invention, a flat portion is in some cases formed on the outer periphery of the optical element array sheet to achieve an object, that differs from the object of holding the optical element array sheet, more specifically, that is, to increase the adhesion with a sheet polarizer that is applied to this optical element array sheet. In the case of this optical element array sheet, a trough is formed at the border between optical elements that are arranged at the edge portion of the periphery of the optical element array sheet and the flat portion that is formed adjacent to these optical elements. This trough is formed in the shape of a steep-sided trough in which one side-wall is formed as a curved surface by the optical elements and the other side wall that confronts this side wall is formed as a vertical surface that is parallel to the thickness direction of the optical element array sheet.
Then, to achieve bonding such that air pockets do not occur in the adhering surfaces of the optical element array sheet and the display panel, sufficient pressure must be applied against the optical element array sheet when the optical element array sheet that is held on the optical element retaining head is adhered to the surface panel Accordingly, when the optical element array sheet that relates to the present invention, such as shown in FIG. 3, is used for mounting on a display panel, the pressure applied to the optical element array sheet from the optical element retaining head during bonding causes deformation of the optical element array sheet at the trough that is located at the border between optical elements that are arranged at the outer periphery of the optical element array and the flat portion that is adjacent to these optical elements as shown in FIG. 13A. The problem therefore arises that, with this deformation in the trough portion, stress concentration occurs and cracking 501 occurs from the bottom of the trough as shown in FIG. 13B.
In the optical element array sheet that relates to the present invention, the lack of precise positioning marks complicates precise bonding of the optical element array sheet and the display panel.